Effect of the geometry and pattern of the flow channel on the performance of polymer electrolyte membrane fuel cell

This research focuses on the effect of the geometry and patterns of the gas flow channel on the PEM fuel cell performance. Simulation was conducted and the results were verified by experiments. Three-dimensional, single phase, compressible and isothermal models of 5 cm² electrodes, anode and cathode, were developed and studied by utilizing a commercial Computational Fluid Dynamics (CFD) software, FLUENT 4.5. Two types of gas flow channel were investigated: conventional and interdigitated. The results showed that the flow channel pattern does not have a significant effect on the anode cell performance, whereas it has a strong effect/influence on the cathode cell performance. The interdigitated design provides a higher limiting current density and cell performance than the conventional design on the cathode side. Moreover, the cell performance does not depend on the inlet and outlet channel widths. On the contrary, for the interdigitated design, it was influenced by the shoulder width. Finally, experiments were conducted to validate the simulation results.     

Modeling and simulation of hard-particle interaction in head/disk interfaces

A hard particle interacting with a slider and a disk in the head/disk interface of hard-disk drives can produce a scratch on the disk and result in data loss. Our work emphasizes modeling and simulation of slider, particle, and disk interactions, scratch generating mechanisms, and linking of scratch to interface design parameters. Two models are presented. The Monte Carlo method was used to calculate scratch probabilities and parametric studies were performed to determine the effect on scratch probability of various parameters, such as friction coefficients, particle mean size, slider wall angles, the ion-milling (IM) etch depth from the air-bearing surface (ABS) of the slider, and the efficacy of additional ABS structures acting as particle shields. Simulation results show that the friction coefficient is a dominant parameter. If the disk friction coefficient is smaller than the slider friction coefficient, scratches are not produced. Using shallow IM depths is an effective and practical way to reduce the scratch probability. Experimental results are very close to the simulation predictions.     

Easy,Green and Safe Carbonylation Reactions through Zeolite‐Catalyzed Carbon Monoxide Production from Formic Acid

Zeolites with the right shape and acid site density and strength, such as certain ZSM‐5 forms, were able to cleanly decompose formic acid to carbon monoxide (CO), and the latter could be directly used in palladium‐catalyzed carbonylation reactions. A simple two‐reactor system was designed to produce CO conveniently and then further react this gas in a safe way. The two‐reactor system is particularly cheap, easy to set up and use. In addition, the carbonylation conditions without pressure allowed for very efficient CO incorporation, with only 1% of palladium(II) chloride (PdCl₂) and Xantphos.

     

Cell-mediated immunity imbalance in pregnancy-induced hypertension

Pregnancy is associated with modifications in the maternal immune system that may be involved in the absence of rejection of the fetoplacental graft characterized by the presence of paternal antigens. This active and specific tolerance towards the fetoplacental unit seems to be compromised in pregnancy-induced hypertension (PIH). To evaluate whether the immunological state in patients with PIH is altered with respect to normal pregnant women we studied 15 patients with PIH, 15 uncomplicated pregnant and 10 healthy nonpregnant women using monoclonal antibodies directed to specific lymphocyte antigen determinants, cytokines (TNF) and soluble molecules (sIL-2R, sCD8). The percentage of CD4 lymphocytes and of natural killer (NK) cells was significantly higher in PIH patients compared to controls (CD4: 42.9 +/- 10.5 vs. 32.7 +/- 12.5%; p < 0.05; NK: 14.7 +/- 6.3 vs. 8.3 +/- 3.4%; p < 0.01). However, these values did not differ when compared to normotensive nonpregnant controls (CD4: 53.1 +/- 5.9%; NK: 17.2 +/- 7.1%). In addition, the soluble IL-2 receptor (sIL-2R) was higher in PIH patients when compared to control patients (725.5 +/- 194.2 vs. 482.5 +/- 187.2 U/ml; p < 0.01). The immune response observed in normal pregnancies responsible for the tolerance towards the fetoplacental unit seems to be altered in PIH patients as suggested by higher levels of CD4 and NK cells, and sIL-2R. This may lead to a chronic rejection syndrome and be involved in the pathophysiology of PIH.     

Preparation of graphite composite bipolar plate for PEMFC

This research studied the preparation of graphite composite using liquid thermosetting plastic such as polyester resin (POE), phenolic modified alkyd resin (PhA) and mixed resin (POE with 10% PhA) as a binder. The morphology, physical, electrical and mechanical properties of the graphite composites were analyzed. The results showed that POE could combine with graphite powder (the 66% wt. saturated of graphite powder) better than PhA and mixed resin and gave higher electrical conductivity (4.52 S/cm). It was also found that epoxy resin could improve the mechanical property of composite plate. The addition of TiO₂ and ZnSt slightly decreased the electrical conductivity and the water absorption. Moreover, it was proposed that TiO₂ could improve the mechanical property. Carbon fiber can increase electrical and mechanical properties and water absorption of the composite with POE as a binder. The mixing of wet-lay mixture with graphite, carbon fiber and POE composite improved the mechanical property and decreased the water absorption.     

Quality of CFD models for jet flow analysis for the design of burners and boilers

CFD models are increasingly used for the design and optimisation of boiler combustion chambers. Numerous commercial codes are available, and the user is confronted with making a proper choice for a particular application. In this paper, the accuracy and effectiveness of the popular code FLUENT™ is investigated in terms of the different turbulence models and numerical schemes that are bundled in the software. The tests are performed for different simple experiments, involving classical hydrodynamic conditions with no combustion. The conclusion of these tests involves also the additional criterion of the computational time required for achieving a reasonable accuracy.     

Optimum condition of membrane electrode assembly fabrication for PEM fuel cells

The aim of this research was to study the effect of fabrication factors on the performance of MEA of a PEM fuel cell. The MEA was prepared by using 5 cm² of porous electrodes with Pt loading 1 mg/cm² and Nafion 115 membrane from Electrochem Co. Ltd. The studied factors were temperature, pressure and time of compression in the range of 130–150 ‡C, 50–100 kg/cm² and 1–5 minutes, respectively. A 2^k factorial design was conducted in this study. The results showed that interaction between pressure and temperature and interaction between temperature and time of compression have significant effects on the performance of the MEA. With low pressure, but high temperature and long compression time, current density is increased. The results showed that the optimum condition was 65 kg/cm², 137 ‡C and 5.5 min of compression time. It was also found that the force of 69 kg-cm for assembling the single cell gave the best performance.     

Production of pure ethanol from azeotropic solution by pressure swing adsorption

Pressure swing adsorption (PSA) is attractive for final separation in the process of water removal especially for fuel ethanol production. Despite many researches on simulation and experimental works on adsorption of water on 3A zeolite in a fixed bed, none have studied a process with the actual PSA system. The purpose of this research was to study the PSA process with two adsorbers and effects of several parameters. The research also included analysis of kinetic and thermodynamic data of ethanol-water adsorption on commercial 3A zeolites in a single fixed bed. A two-level factorial design experiment was used in this research work to preliminarily screen the influence and interaction among the factors. Effects of important parameters such as initial temperature, feed concentration and feed rate were investigated. It was proven that the Langmuir isotherm could best predict the experimental results. In the PSA pilot test, the principal factors, which had effects on the performance, were feed rate, feed concentration, adsorption pressure and the cycle time. Prediction of the process efficiency in terms of ethanol recovery and enrichment was proposed in the form of regression models. The results of the study in a fixed bed adsorber could help designing a pilot-scale PSA unit. The experiments proved to be successful in terms of producing high concentration ethanol with high percentage of ethanol recovery. With further simulation work the process could be scaled up for an industrial use.